High-strength steel sheets have been commonly used as a material for automotive members, for example, in order to reduce the weights of the members. For example, frame members and crash-resistant members are required to be resistant to deformation at the time of impact in order to ensure the safety of vehicle occupants. Accordingly, a steel sheet used as a material for these members is required to have a high yield ratio. In order to consistently perform press forming of the steel sheet into a shape without the occurrence of cracking, the steel sheet is also required to have a reduced difference in tensile strength between the center and edges of the steel sheet in the width direction. There have been disclosed various steel sheets and techniques for producing the steel sheets in response to the yield ratio requirement.
Patent Literature 1 discloses a high-strength steel sheet having excellent paint-baking hardenability, the steel sheet containing Nb and Ti at a content of 0.01% or more in total and including a main phase that is ferrite having a recrystallization ratio of 80% or more, and a method for producing the high-strength steel sheet. Patent Literature 2 discloses a high-strength steel sheet having excellent collision resistance, the high-strength steel sheet having a microstructure including 20% to 50% unrecrystallized ferrite, and a method for producing the high-strength steel sheet.